A spinstand is a device for testing magnetic heads and magnetic medium-bearing disks for disk drives. A disk drive is a device having one or more magnetic medium-bearing disks installed on a spindle for rotation, and one or more magnetic heads flying over the surface of the disks reading data from and writing data onto those disks.
FIG. 1 shows a top plan view and a side view, partially cutaway, respectively, of a prior art spinstand 100. The spinstand 100 includes a base plate 102, a spindle assembly 104 including a rotor 110 and adapted for rotational motion about a spin axis 122. The spinstand further includes a rotary encoder 140 rigidly coupled to the rotor 110, stationary encoder reader 103, a chuck 112 supporting a disk 118, a precision head positioning mechanism 108 with attached X and Y linear position encoders 145 and 146 for absolute positioning of the head 116 over the disk, and a controller 105 for coordinating and controlling the functional operation of the device.
The spindle assembly 104 includes a rotor 110 (with an associated drive motor, not shown) mounted on the base plate 102.
The encoder 140 is rigidly coupled to the disk through rotor 110, and rotates about the spin axis of the spindle. The encoder 140 provides signals representative of the absolute angular position of the rotor 110 (and thus disk 118) at any given moment, during spinning of the disk or when the disk is stopped.
The precision head positioning mechanism 108 selectively positions a magnetic head 116, over the magnetic medium-bearing disk 118 supported by the chuck 112 of spindle assembly 104.
The precision head positioning mechanism 108 provides the absolute position of the head 116 in XY system of coordinates. The position of the spin axis 122 is also known in the same XY system of coordinates. The angular position of the disk 118 is determined by the rotary encoder 140 and therefore the location of any point on the disk 118 can be expressed in polar system of coordinates having the center of coordinate system at the spin axis 122. The location of that point of the disk 118 can also be converted to the XY system of coordinates, such that the position of the head in respect to that point on the disk can be determined at any given time.
Disk 118 is supported in a horizontal plane, clamped to a support surface S of spindle 104 by chuck 112. Disk 118 is clamped to spindle 104, for example by vacuum clamping (in the manner shown in U.S. Pat. No. 7,295,002). The spindle 104 is driven to rotate the disk 118 about spin axis 122 extending perpendicular to the plane of the disk 118.
There are several applications when a magnetic medium-bearing disk has pre-written or pre-printed data. In these applications the disk 118 includes a plurality of circular concentric data tracks on its magnetic medium-bearing surface, exemplified by track 124. When disk with pre-written or pre-printed data is placed on the spindle, the axis of concentricity of the data tracks (data axis) and axis of the spindle (spin axis 122) in general do not coincide due to mechanical tolerances. This creates a problem to follow the tracks. In such cases, particularly in disks with closely placed data tracks, the magnetic head positioning assembly of the spinstand might not be able to accommodate such offsets and perform the required testing functions with sufficient accuracy. Following of tracks in a presence of a large eccentricity makes it difficult and in some cases impossible because of unbearable load on the servo system used to position head 116 over the disk 118. It makes accurate measurements impossible in various applications.
An example of such an application is testing the disks where servo information is pre-printed using discrete track recording (DTR) technology.
In other applications, spinstands are used for data recovery and failure analysis, for example, when a disk with pre-written information is removed from a failed disk drive. For such an application, placing a removed disk on a spinstand, while providing minimal data track eccentricity with respect to the spin axis, is as important as in the case of testing Discrete Track Recording (DTR) disks. Data recovery and failure analysis are possible with higher degree of integrity if eccentricity is reduced.
Reducing eccentricity is beneficial for the disk drives as well. When DTR media with pre-printed servo information are assembled in a disk drive, it is important to mount the disk on a disk drive spindle with minimal data track eccentricity. Track following is possible with greater accuracy if eccentricity is reduced.
It is beneficial to reduce eccentricity by aligning the data axis of a disk with the spin axis of a spinstand or a drive.
Various devices are available in the prior art, which purport to center a disk using the inner diameter or outer diameter of the disk, e.g. as shown in U.S. Pat. No. 6,421,199. The method of that patent assumes that data tracks are essentially concentric to the outer edge of the disk, which is generally not true. This method provides accuracy couple of orders of magnitude lower than required.
The present invention provides a centering method and system for alignment of a data axis with a spin axis based on the information written on the disk, achieving a high degree of accuracy, on the order of several angstroms.